The impact of megafaunal loss and climate change on ecosystem functions in aridland ephemeral river systems

短暂河流系统是指一年中最多只有几个星期可见的水。这通常是因为它们位于炎热干燥的气候中，降雨量很少。因此，它们对人类和野生动物社区都是无价的，因为它们从其他来源获得的水相对稀缺。纳米比亚有12条这样短暂的河流贯穿全国，这些河流支持丰富而独特的植被，提供农业服务，并作为迁移和地方性巨型动物种群的绿洲（Jacobson et al，1995）。不幸的是，魅力十足的巨型动物（重于1000公斤的陆生脊椎动物，Owen-Smith，1988年）现在在纳米比亚的大部分河流中是一种罕见的景象，主要是由于狩猎和其他人与野生动物的冲突。从保护的角度来看，这是一个坏消息，但从经济的角度来看，因为野生动物旅游对纳米比亚的收入贡献很大（Jacobson等人，1995年）。然而，它确实为实验提供了一个独特的机会。由于相似的河流系统中有一些存在巨型动物，而另一些则没有，我们可以比较河流之间生态过程的差异，具有相对明确的因果关系。我的博士学位涉及使用遥感数据调查这些河流系统之间的差异。它也应该产生新的数据，某些大型动物使用这些系统的生态作用，特别是大象和长颈鹿。气候影响的建模也是这项研究的关键组成部分，原因有二。第一个问题涉及旱地短命河流系统的普遍性，因为气候变化导致的降雨频率和强度的预期变化可能会促使其他临时河流被归类为“短命”河流（Larned等人，2010年; Tooth和Nanson，2011年）。第二个是气候与生态系统的关系。预计的降雨量变化如何影响短暂的河流水文学可能会有所了解，但所述变化如何影响含水层依赖的生态系统内的生态过程还没有（Eamus等人，2006年; Colvin等人，2007年）。因此，调查这些系统中的降雨变化是本项目的组成部分。

Ephemeral river systems refer to rivers that only visibly contain water for a few weeks in a year, at most.This is usually because they are situated in hot, dry climates with very little rainfall. As such they areinvaluable to communities of humans and wildlife alike, because of the relative scarcity of water availableto them from other sources. Namibia has 12 of these ephemeral rivers running through the country, whichsupport rich and unique vegetation, provide agricultural services, and act as an oasis for migrating andendemic megafauna populations (Jacobson et al , 1995).Unfortunately, charismatic megafauna (terrestrial vertebrates heavier than 1000kg, Owen-Smith, 1988) isan uncommon sight in most of the Namibian rivers now, largely due to hunting and other human-wildlifeconflicts. This is bad news from a conservation perspective, but also from an economic perspective, aswildlife tourism contributes a significant amount towards Namibia's revenue (Jacobson et al , 1995). Itdoes provide a unique opportunity for experimentation, however. With similar river systems havingmegafauna persist in some but not others, we can compare the disparity of ecological processes betweenthe rivers, with relatively clear cause and effect.My PhD involves investigating the differences between these river systems using remote sensing data. Itshould also yield new data on the ecological roles of certain large animals using these systems,particularly elephants and giraffes.Modelling of climate effects are also a key component of this study for 2 reasons. The first pertains to theprevalence of ephemeral river systems in drylands, as expected changes to rainfall frequency and intensity,resulting from climate change, may drive other temporary rivers to become classed as 'ephemeral'(Larned et al, 2010; Tooth and Nanson, 2011). The second pertains to the relationship between climateand ecosystem. How the projected rainfall changes influence ephemeral river hydrology may be somewhatunderstood, but how said changes influence ecological processes within aquifer dependent ecosystems arenot (Eamus et al, 2006; Colvin et al, 2007). Thus, investigating rainfall change in these systems is integralto this project.